1. Field of the Invention
The present invention relates to a signal reproduction apparatus and method in which a signal transmission between a rotary side and a fixed side of a rotary head apparatus is carried out via a rotary transformer and in particular, to a signal reproduction apparatus and method involving a rotary drum having a reproduction amplifier.
2. Description of the Prior Art
In a DAT (digital audio tape recorder), VTR, and the like, a so-called helical scan type rotary head apparatus is known. FIG. 1 shows a brief configuration of such a helical scan type rotary head apparatus as an example, including a rotary drum 51 and a fixed drum 52. A magnetic head 53 for recording and reproduction is arranged so as to be exposed through a window 54 at the outer circumference of the rotary drum 51.
FIG. 2 shows a guide running state of a magnetic tape 55. The magnetic tape 55 is guide and driven to run in an inclined direction along the outer circumference of the rotary drum 51 and the fixed drum 52. The magnetic head of the rotary drum 51 carries out recording/reproduction while scanning the magnetic tape 55 in an inclined direction with respect to the tape running direction.
Transmission of a recording/reproduction signal for the recording/reproduction head of the rotary drum is carried out via a rotary transformer. A recording output amplifier and a reproduction initial stage amplifier are normally arranged outside of the drum.
FIG. 3 is a block diagram showing a circuit for connection between the recording/reproduction head of the rotary drum and the recording/reproduction amplifier. In FIG. 3, reproduction heads 61, 62 arranged at the rotary side such as the aforementioned rotary drum are respectively connected via windings 71, 72 of the rotary transformer 70 to reproduction initial stage amplifiers 81, 82 of the fixed side, whereas recording heads 63, 64 of the rotary side are respectively connected via windings 73, 74 of the rotary transformer 70 to recording amplifiers 83, 84 of the fixed side. It should be noted that in FIG. 3, each of the windings of the rotary transformer 70 is denoted by a reference numeral having a subscript "a" for the fixed side and a subscript "b" for the rotary side.
FIG. 4 is a cross sectional view showing the rotary transformer 70 as an example including a fixed side core 70a and a rotary side core 70b which are arranged to oppose each other via a clearance. Each of the cores, as shown in FIG. 5, has a number of concentric circular grooves 76 corresponding to a number of recording/reproduction channels formed on the opposing sides. The windings 71b to 74a are mounted in the grooves of the fixed side and the windings 71b to 74b are mounted in the grooves of the rotary side. In the rotary transformer 70 having the aforementioned configuration, the clearance present between the cores 70a and the 70b causes a large transmission loss compared to a transformer having no clearance.
The transmission loss of this rotary transformer 70 results in a reduction of a weak reproduction head output signal, which in turn reduces the signal ratio with respect to an amplifier noise, so-called SN ratio, deteriorating the quality of the amplifier output signal.
Next, FIG. 6 shows a circuit configuration equivalent to a circuit from the reproduction head to the reproduction initial stage amplifier. A signal source 81 represents a reproduction head electro motive force voltage v.sub.1, and a coil 82 represents a head inductance L. A capacitor 83 represents a capacity C as a total of the amplifier input capacity, the wiring capacity, and the rotary transformer capacity. A resistor 84 represents a resistance component in parallel to the head L in addition to a parallel synthesis value R of a damping resistance. These are connected to an input side of the reproduction initial stage amplifier 85.
As is clear from this FIG. 6, the head inductance L and the capacity C at the amplifier input terminal constitute a low pass filter. This low pass filter brings about a cut-off frequency .omega..sub.0 having a characteristic as shown in FIG. 7 which determines an upper limit of a frequency band of this system. It should be noted that the aforementioned cut-off frequency .omega..sub.0 is, for example, as follows: EQU .omega..sub.0 =1/(LC)
The capacity C obtained at the amplifier input side includes an input capacity of the amplifier itself to which is also added a capacity parallel to the windings of the rotary transformer as well as the winding capacity between the head and the rotary transformer and between the rotary transformer and the amplifier, which may be greater than the input capacity of the amplifier itself, limiting the frequency band.
To cope with this, there is a case when the reproduction initial stage amplifier is provided on the rotary drum.
This make it possible to eliminate attenuation of the reproduction signal due to the aforementioned loss in the rotary transformer as well as to reduce the capacity of the amplifier input side, extending the frequency band.
That is, FIG. 8A shows a case when a reproduction initial stage amplifier 104 is provided at the fixed side. In this case, between a reproduction head 101 and a reproduction initial stage amplifier 104, there are connected in parallel the rotary transformer 102 and a cable 103. FIG. 8 B shows a case when a reproduction initial stage amplifier 112 is provided at the rotary side. In this case, a reproduction head 111 is provided in the vicinity of a reproduction initial stage amplifier 112, in which the amplifier input side has a capacity which is almost determined by the input capacity of the amplifier itself, increasing the cut-off frequency of the low pass filter, which in turn extends the frequency band. The output of the reproduction initial stage amplifier 112 is fed to the rotary transformer 113 and via a cable 114 to the next stage amplifier.
In the aforementioned case when the reproduction initial stage amplifier is provided at the rotary side, it is necessary that the amplifier operation power source power be supplied to the rotary drum side. For this, there is a known technique for transmitting power via the rotary transformer.
In this case, as shown in FIG. 9, a power transmission channel is added besides the recording/reproduction channels. That is, a power signal from a power supply driver 121 is supplied via windings 122P of a rotary transformer 122 to a rectifier circuit 123 for power supply via a smoothing voltage stabilizing block 124 to a reproduction initial stage amplifier 126. The reproduction initial stage amplifier 126 amplifies a reproduction signal from a reproduction head 125 and transmits the amplified signal via the rotary transformer 122 to the fixed side.
FIG. 10 shows a configuration example of the power supply driver 121 shown in FIG. 9. Power from an AC power source 131 is supplied via a CMOS driver circuits 132 and 133 to the fixed side winding of the rotary transformer. Respective portions a to e in FIG. 10 have signal waveforms as shown respectively in FIG. 11A to FIG. 11E. FIG. 11F shows a push-pull output from the two CMOS driver circuits 132 and 133 supplied to the fixed side winding of the rotary transformer, which is equivalent to a difference between the aforementioned signals c and e, i.e., c-e.
However, the configuration as shown in FIG. 9 has a problem that a signal in the power transmission channel, passing through the rotary transformer windings or air, reaches the recording/reproduction signal system, lowering the signal noise ratio. Especially, this significantly affects the reproduction head output which is a weak signal.